The invention concerns a high frequency surgery apparatus for cutting and/or coagulating biological tissue comprising at least one high frequency generator which in operation forms a high frequency circuit with the tissue to be treated with the formation of an arc.
The invention further concerns a method of operating a high frequency surgery apparatus, wherein for cutting and/or coagulating biological tissue a high frequency circuit is formed between at least one high frequency generator and the tissue to be treated, with the formation of an arc.
The term high frequency surgery is used essentially to denote cutting and coagulating (sclerosing) biological tissue using high frequency currents (about 0.2 MHz to 3 MHz). In that respect the cutting effect in biological tissue is based on the formation of an arc between an active electrode and the tissue. To achieve a cut which is as uniform as possible, with constant haemostasis (cutting result) the arc parameters are used as a regulating criterion for the high frequency generator.
In coagulation the high frequency current is used for haemostasis or for the ablation of tissue. In that case the tissue surrounding the electrode is heated by the current to such an extent that body-specific albumins break down and stick together and intracellular as well as extracellular fluids vaporise. That results in denaturing and shrinkage of the tissue and the blood vessels and thus ultimately stopping of hemorrhages. In ablation a tissue region which is to be destroyed or removed from the body is denatured in that way. The tissue region treated in that way heals up and is broken up by body-specific processes without having to be removed by an operative procedure.
In the cutting operation arcs are produced through a vapour layer of cell fluid between a cutting electrode and the tissue. The point concentration of the high frequency current in the arc gives rise to a flash-like increase in the temperature of the cellular tissue, which leads to abrupt vaporisation of the cell fluid and ultimately cell explosion. The cutting effect occurs due to the distribution of the arcs as they ignite over the active electrode, wherever the vapour layer between the tissue and the electrode is sufficiently thin. In that case electrically conductive tissue can be severed virtually without mechanical pressure. Due to the high temperatures the risk of germs being spread is reduced, in addition at the same time it is possible to achieve coagulation of surrounding pieces of tissue.
The monopolar procedure involves the use of an active coagulation or cutting electrode and a neutral electrode which is applied over a large area. In that case the high frequency current flows from the active electrode to the neutral electrode by way of the tissue to be treated. The crucial consideration for the thermal action of the current at the application placement is an active electrode of small area, in relation to a neutral electrode of large area. That provides for a high current density and thus a substantial increase in the temperature of the tissue at the operation location and at the same time avoids unwanted tissue damage at the neutral electrode.
Bipolar applications involve the use of two evenly matched electrodes which are combined in one instrument. In that case the high frequency current flows from the one electrode of the surgical instrument to the other electrode thereof by way of the tissue to be treated. Alternatively the electrodes can also be provided on different units. The best-known instruments in that respect are coagulation forceps with which blood vessels can be specifically and targetedly gripped and then closed.
In the present document the arc intensity is defined as a measurement in respect of the frequency of occurrence and the number of ignited arcs. It is proportional to the power which is converted at the arc for spark flash-over and for maintaining the vapour layer. With a constant power delivery from the HF generator arc intensity depends on parameters such as cutting depth, cutting speed and tissue factors. Regulation of the arc intensity is used to achieve cutting results which as far as possible are independent of the tissue factors and cutting parameters. In that respect the term cutting result is used to denote the degree of coagulation (desired) and the degree of carbonisation (carbonisation: unwanted material or tissue carbonisation) of the cut surfaces.
Biological tissue is not a homogeneous mass. Muscle, fat and other kinds of tissue as well as blood vessels alternate. The speed and the depth of penetration of the electrode also change during the cutting operation. As a result the electrical conditions under which the cutting electrode is guided are constantly changing. HF generators without arc regulation cannot adapt their electrical output parameters to those variable use conditions. In the case of a cutting operation the active electrode is surrounded by a film of vaporised cell fluid. The vapour layer is compressed and displaced by virtue of the advance movement in the region in front of the electrode. It is there that the arcs are ignited in the case of an optimum cutting operation due to the thinner vapour layer. With an excessively high power output from the HF generator the arcs are ignited distributed over the entire electrode surface.
The desired result in the case of a cut made with an HF surgery apparatus is tissue separation in which the cut surfaces are coagulated but not carbonised. An excessively high power delivery from the HF generator does not lead to an improved cutting result but an increased level of arc intensity. That involves more severe necrosis and carbonisation of the cut surfaces. That delays the healing process and is therefore absolutely to be avoided. In contrast if the power is too low an arc can no longer be ignited and the cutting operation comes to a halt.
Commercially available HF generators regulate the output voltage of the generator to keep the arc intensity between the cutting electrode and the tissue constant. With that regulating system the output power of the HF generator can be substantially better adapted to the prevailing operative requirements than with constant voltage regulation or completely without regulation. In the case of an ideal HF surgery apparatus the cutting result would always be constant and reproducible under all conditions. It is here that previously technically implemented arc regulating systems meet their limits for there is a marked residual dependency in respect of the degree of coagulation and carbonisation of the cut surfaces for example on the cutting speed and the cutting depth.
Technical recognition of the tissue in which the operator is cutting considerably increases the level of certainty when using HF surgery. In the ideal case the surgery apparatus should detect the kind of tissue in which the operation is to be carried out and should shut down or react with signalling as soon as the cutting electrode comes into contact with other pieces of tissue in order to avoid unwanted damage thereto.
High frequency surgery apparatuses and methods of operating same are known from the state of the art.
DE 25 04 280 describes for example an apparatus for cutting and coagulating human tissue with high frequency current, which is regulated on the basis of the state of the cutting or coagulating procedure.
Detecting arc intensity for controlling a high frequency generator is set forth in DE 195 42 418.
A high frequency generator with tissue differentiation on the basis of a current-voltage characteristic measured at a high frequency generator is described in DE 195 42 419.
DE 28 01 833 shows an electrosurgical cutting apparatus in which a regulator for the HF voltage of the HF generator responds to a DC voltage which is produced in the cutting operation.
DE 41 26 607 describes an arrangement for cutting biological tissue with high frequency current.
The problem with the known high frequency surgery apparatuses and the control methods thereof is that different cutting results can occur because there is a dependency on the parameters determined by the operator such as for example cutting speed and cutting depth and the kind of tissue, such as for example muscle tissue or fat tissue.